Patent GB-745063-A (GB)
Title: Adipic acid crystallization
IPC: C07C51/43
Filed: 1953-03-10
Abstract: <PICT:0745063/IV(a)/1> Adipic acid is crystallized from a reaction mixture obtained by oxidation of a cyclic hydrocarbon or a mixture of cyclic hydrocarbons by air and/or nitric acid, the crystallization being carried out in a continuous manner at a temperature of from about 350 DEG  C. to about 70 DEG  C., without substantial nucleation, from a supersaturated solution derived from the oxidation products and containing, on an adipic acid free basis, from 8 to 18 per cent by weight of the by-product dibasic acids.  The solution should preferably have an adipic acid supersaturation of 2 DEG  C. to 5 DEG  C.  In the procedure illustrated in the Figure a solution is saturated with adipic acid in vessel 1 and the saturated solution is forced by pump 2 through filter 3 and rotameter 4 into the supersaturator 5 where the temperature of the solution is lowered by means of a circulating cooling medium to give the desired degree of supersaturation.  The supersaturated solution flows by pipe 5a through the crystallization chamber 6 which is provided with a heating coil and contains in its bottom portion a porous seed basket 7 in which the crystals are collected.  The mother liquor is returned from the top of crystallization chamber 6 to the saturator 1 by the pipe line 6a.  The pipe line 6b in conjunction with the valves on pipe lines 5a and 6a enable the crystallization chamber 6 to be bypassed and the solution to be sent back to the saturator vessel 1. The outlet 8 of the crystallization chamber is connected to a source of vacuum.  In examples for determining the rate of crystal growth a saturated solution prepared by saturating a nitric acid mother liquor with adipic acid is placed in the saturator 1 while a weighed quantity of adipic acid seed crystals with known surface area characteristics is placed in the seed basket 7.  The flow rate, liquor temperature in the crystallization chamber and in the saturator are taken and the seed basket weighed at intervals so that a record of weight gain versus time is obtained.  The nitric acid mother liquor is the mother liquor left after crystallization of the first crop of adipic acid crystals from the product obtained by air and nitric acid oxidation of cyclohexane as described in Specification 633,354, after stripping off the volatile matter.  The crystallization linear growth rate is calculated in each case and tabulated results are given to show the effect of the crystallization temperature, the degree of supersaturation, and the presence of monobasic acids and dibasic acids on the crystal growth rate.  The results relate to feeds containing 47 and 43 per cent nitric acid and 12 or 8 per cent dibasic acids (glutaric and succinic acids) together with in some cases small amounts of acetic, valeric or caproic acids.ALSO:<PICT:0745063/III/1> Adipic acid is crystallized from a reaction mixture obtained by oxidation of a cyclic hydrocarbon or a mixture of cyclic hydrocarbons by air and/or nitric acid, the crystallization being carried out in a continuous manner at a temperature of from about 35 DEG C. to about 70 DEG C., without substantial nucleation, from a supersaturated solution derived from the oxidation products and containing, on an adipic acid free basis, from 8 to 18 per cent by weight of the by-product dibasic acids.  The solution should preferably have an adipic acid supersaturation of 2 DEG C. to 5 DEG C.  In the procedure illustrated in the Figure a solution is saturated with adipic acid in vessel 1 and the saturated solution is forced by pump 2 through filter 3 and rotameter 4 into the supersaturator 5 where the temperature of the solution is lowered by means of a circulating cooling medium to give the desired degree of supersaturation.  The supersaturated solution flows by pipe 5a through the crystallization chamber 6 which is provided with a heating coil and contains in its bottom portion a porous seed basket 7 in which the crystals are collected.  The mother liquor is returned from the top of crystallization chamber 6 to the saturator 1 by pipe line 6a.  The pipe line 6b in conjunction with the valves on pipe lines 5a and 6a enable the crystallization chamber 6 to be by-passed and the solution to be sent back to the saturator vessel 1.  The outlet 8 of the crystallization chamber is connected to a source of vacuum.  In examples for determining the rate of crystal growth a saturated solution prepared by saturating a nitric acid mother liquor with adipic acid is placed in the saturator 1 while a weighed quantity of adipic acid seed crystals with known surface area characteristics is placed in the seed basket 7.  The flow rate, liquor temperature in the crystallization chamber and in the saturator are taken and the seed basket weighed at intervals so that a record of weight gain versus time is obtained.  The nitric acid mother liquor is the mother liquor left after crystallization of the first crop of adipic acid crystals from the product obtained by air and nitric acid oxidation of cyclohexane as described in Specification 633,354 [Group IV(b)] after stripping off the volatile matter. The crystallization linear growth rate is calculated in each case and tabulated results are given to show the effect of the crystallization temperature, the degree of supersaturation and the presence of monobasic acids and dibasic acids on the crystal growth rate.  The results relate to feeds containing 47 and 43 per cent nitric acid and 12 or 8 per cent dibasic acids (glutaric and succinic acids) together with in some cases small amounts of acetic, valeric or caproic acids.